There are numerous applications where it is necessary to penetrate a sealed container with one or more electrical leads so as to provide electrical access to and from electrical components enclosed within. One such application for which the present invention has particular but not limited utility is in body implantable pulse generators (e.g., for the treatment of bradycardia, tachycardia or nerve stimulation), referred to generally herein as implantable pulse generators (IPG's). Typical devices of this type are formed of a metal container housing the electrical power source components of the IPG with a lid or the like welded to the container to close the device and provide it with a hermetic seal.
An electrical lead or pin is electrically connected to the IPG by means of attachment to one or more feedthroughs which penetrate the container but maintain the hermetically sealed environment thereof. A typical feedthrough consists of an external metal part, or frame or ferrule, into which an insulator solid part typically formed of glass, ceramic, or glass and ceramic is sealed. Within the insulator, one or more metal leads or pins are sealed. Since the reliability of critical implantable medical devices depend on hermetic sealing of various components, the integrity of such seals is of paramount importance.
In many implantable devices, metals which have long term corrosion resistance and biocompatability are needed to provide years of reliable service since maintenance or repair possibilities for the devices are extremely limited. Moreover, since such devices are sometimes lifesaving for the patient, failures of the hermetic seal materials can have catastrophic consequences.
Wire fabricated by drawing or forming processes often contains anomalies such as drawlines, cracks or seams. See FIG. 1, where an example of a prior art drawn wire having defects such as cracks and longitudinal seams is shown.
It is a common practice to incorporate wire as conductors in glass-to-metal and ceramic-to-metal seals. The wire anomalies described above can induce the loss of hermeticity in such seals if the orientation of such anomalies is parallel to the seal cross-section. Deep or narrow anomalies in wire are difficult to completely fill with either glass or solder-braze alloys that typically form the types of hermetic seals described above. Deep or narrow anomalies may also act as stress-risers, such that application of thermal or mechanical loads to the seal can induce latent hermetic failure.
The inability of manufactures to routinely produce wire free from the anomalies described above makes it difficult to produce reliable hermetic seals. The inability of wire manufacturers to consistently meet the surface requirements for hermetic seal applications conflicts directly with the opposing requirement for highly reliability components in implantable medical devices.